The effect of microstructure and mechanical properties on sliding wear and cavitation erosion of plasma coatings sprayed from Al2O3+40 wt% TiO2 agglomerated powders

This paper discusses the influence of 40 wt% TiO2 addition to Al2O3 and the selection of plasma spray parameters on the morphology, microstructure, microhardness and adhesion of coatings. Mainly, the tribological behavior and cavitation erosion performance of produced coatings were evaluated. First, the two-factorial design of the experiment, with the stand-off distance and torch scan speed as variables, was used to plan coating deposition by means of atmospheric plasma spraying (APS). Then, a process response using a multiple regression method was used to investigate the influence of factors variation on coatings functional properties. Although these properties were already investigated in alumina-titania coatings, there are still some knowledge gaps. Particular attention was given to the composition of Al2O3 + 40 wt% TiO2 , because, so far, it is the most rarely discussed in the literature in terms of, e.g., cavitation or wear resistance. Increasing the torch scan speed and decreasing the spraying distance densifies the microstructure and increases coating's mechanical properties. A dense and low porosity structure facilitates cavitation erosion resistance and minimizes friction coefficient. Cavitation erosion damage relies on brittle cracking initiated at coatings porosity. Therefore, coatings with decreasing porosity show layer-like removal contrary to uniform material removal stated for porous coatings. The sliding wear mechanism has been dominated by abrasive wear and fatigue cracking. Accumulated wear debris undergoes adhesive smearing and removal.